1. Field of the Invention
This invention relates generally to sidelobe cancelling techniques for large-aperture phased arrays, and more particularly to phase-shifter nulling techniques which require no auxiliary elements or correlators or beamformers.
2. Background Description
The particular type of antenna system addressed is a large aperture(in wavelengths) phased array of low-sidelobe design wherein the investment is already considerable, and one simply could not afford to make it fully adaptive. The RADC Space-Based-Radar (SBR) antenna system concept as discussed in "An Experimental Completely Overlapped Subarray Antenna," by H. L. Southall and D. T. McGrath, IEEE Trans. Antennas and Prop., Vol. AP-34, pp. 465-474 (April 1986), is an excellent application case in point. The low sidelobes are necessary for good initial protection against sidelobe interference and large clutter returns. Also, they reduce the problems associated with strong sources, i.e., in regard to the number of adaptive degrees-of-freedom (DOF) required and the dynamic range of the adaptive processor. Thus, retention of the low sidelobes is considered a major requirement for the system.
Several partially-adaptive array techniques have been suggested in the literature for approaching this problem, including the conventional Side-Lobe-Canceller (SLC) configuration shown in "Adaptive Arrays," by S. P. Applebaum, IEEE Trans. Antennas Prop., Vol. AP-24, pp. 585-598, (September 1976), constrained beamspace adaptive systems as described in "Adaptive Nulling with Multiple-Beam Antennas," by J. T. Mayhan, IEEE Trans. Antennas and Prop., AP-26, pp. 267-273, (March 1978), and overlapped sub-array (space-fed lens) configurations as shown in "An Adaptive Low-Angle Tracking System," by E. C. DuFort, IEEE Trans. Antennas and Prop., AP-29, pp. 766-722, (September 1981). A brief commentary on each of these solutions follow: